Recent advances in microelectronics have included the use of high-k films in gate stacks for logic applications. These high-k films often include hafnium (Hf) and/or zirconium (Zr) based oxides/silicates that are deposited on a Si substrate. In addition, advanced gate stacks may include metal gate electrodes that are deposited on the high-k films. The chemical composition of the metal gate electrodes is selected to have the appropriate work functions for N-MOS and P-MOS transistors. While metal gate electrode layers do not need to be doped to be electrically conductive, there is not one metal that can set the appropriate work function for both NMOS and PMOS devices; the energy required to pull an electron free from the surface of the electrode.
One approach for controlling the gate electrode work function includes depositing a composite metal-containing gate electrode layer, where composition of the layer can be adjusted to obtain the desired workfunction of the gate electrode. However, the effective workfunction of a gate stack further depends on bulk and surface material properties, crystallographic orientation, and the permittivity of the high-k film interfacing with the gate electrode layer. In particular, interactions of the different materials at layer interfaces and diffusion of chemical species throughout a gate stack during post-processing can affect the work function and other properties of the semiconductor device. Thus, methods for controlling the gate electrode work function by controlling composition of the gate electrode layer may be ineffective in achieving the desired work function, and new methods are needed for adjusting and controlling the effective work function of semiconductor devices containing high-k materials.